In the related art, as a method of processing the surface of a semiconductor device, an apparatus of etching the semiconductor device by using plasma is widely known. Herein, the related art will be described by using an electron cyclotron resonance (hereinafter, referred to as ‘ECR’) type plasma etching apparatus as an example. In this ECR type, the plasma is generated by microwaves in a vacuum vessel applying a magnetic field from the outside. Electrons perform cyclotron motion by the magnetic field and the plasma can be efficiently generated by resonating a frequency of the magnetic field and a frequency of the microwaves. In order to accelerate ions incident in the semiconductor device, radio-frequency power is applied to a sample as sequential waveforms substantially in a sinusoidal waveform. Herein, the radio-frequency power applied to the sample is, hereinafter, referred to as a radio-frequency bias. Further, as gas forming plasma, halogen gas such as chlorine or fluorine is widely used.
Radical or ions generated by the plasma react with an etched material, such that etching is performed.
A reaction product generated by etching causes reattachment to a pattern and an etching shape thereof is tapered. Therefore, in order to achieve high precision etching, control of the reaction product generated during etching becomes important. A method of shortening a stay time of the reaction product is used in order to reduce the concentration of the reaction product. When a stay time of gas in a plasma processing chamber is set as τ, in the case where P is a processing pressure, V is the capacity of the plasma processing chamber, and Q is a gas flow, τ has a relationship of τ=PV/Q and in apparatus configuration, the limitations of the P, V, and Q are defined. The stay time of the gaseous reaction product may be shortened by lowering a processing pressure or increasing the gas flow on the basis of the relationship, but it is difficult to enhance the increase of the gas flow and the lowering of the processing pressure in a trade-off relationship.
Further, in Japanese Patent Application Laid-Open Publication No. Hei8 (1996)-250479, as a method of controlling the reaction product and increasing etching precision, temporal modulation of the plasma or radio-frequency bias is disclosed. In addition, In Japanese Patent Application Laid-Open Publication No. 2001-85395, the method of controlling the temporally modulated radio-frequency bias in which ion energy is with high precision controlled by dividing the radio-frequency bias into two or more is disclosed.